Definition of triple-negative breast cancer

triple-negative breast cancer (TRIH-pul-NEH-guh-tiv brest KAN-ser): Triple-negative breast cancer is defined by a lack of expression of estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2/neu). Also called ER-negative PR-negative HER2/neu-negative breast cancer and TNBC.